In the past, Stirling-cycle machines have been used to achieve cryogenic temperatures because they have been well-developed and provide reasonable efficiency in this application. Stirling-cycle machines, however, are somewhat unreliable and are subject to vibration which disturbs the detectors being cooled.
In the past, systems using compressors and Joule-Thomson valves have not been used in such practical applications because of the substantially greater power input requirement and lower efficiency of such systems.
The use of cooling systems employing a Joule-Thomson valve has been further complicated by the properties of available working fluids. Nitrogen is a desirable working fluid in many such systems because its properties permit it to operate satisfactorily from room temperature to 77K, and thus permit single-stage systems (i.e., systems using a single working fluid). The extent of cooling available from systems using Joule-Thomson valves, however, depends on the working gas properties at the warm end of the system; and unfortunately, the properties of nitrogen are such that when starting from room temperature, high power inputs have been required to obtain adequate cooling during operation. Thus, in the past, Stirling-cycle machines have been used almost exclusively in cryogenic cooling systems to produce temperatures higher than about 60K.